1. Field of the Invention
This invention relates to the shaping of heat formable material such as heated glass sheets and more particularly to an adjustable press arrangement.
2a. Technical Considerations
Shaped glass sheets are widely used as windows for vehicles such as automobiles and the like. In the fabrication of these windows flat glass sheets are shaped to precisely defined curvatures dictated by the shape and outline of the frames within which the windows are installed. It is important that these windows meet stringent optical requirements and that they be free of optical defects that would tend to interfere with the clear viewing therethrough in the viewing area. Any distortion in the sheet engaging surface of the shaping members is replicated in the major surface of the shaped sheet and may result in an optically defective product.
Oftentimes the curvatures of automobile windows are similar but not identical. As a result, a different bending mold must be used. The amount of time needed to remove the upper mold for one pattern and install a replacement mold for another pattern of a different configuration is considerable and interferes with time that could be used in production. In addition, during heating and shaping of the glass sheets, the mold's press face may warp due to the relative expansion of the materials forming the mold under such a thermal condition. As a result, minor changes in the heated press face configurations may be required to correct for loss of desired curvature. Therefore it is desirable to have a shaping mold capable of producing multiple patterns of different curvature as well as providing an adjustment mechanism that allows for accurate adjustments to the press face.
It is common practice to use an adjustable press face with a flexible pressing surface adjustably secured to a rigid adjusting plate. Bolt and clevice arrangements are welded to the rear facing surface of the press face and extend through a rigid adjusting plate. A pair of nuts positioned on opposite sides of the rigid adjusting plate are used to vertically move the bolt and, in turn, the press face, and lock the adjusted configuration in place. This type of press adjustment arrangement requires adjusting internal portions of the shaping mold, i.e., making adjustments between the press face and the rigid adjusting plate.
It would be advantageous to construct a shaping mold with an adjustable shaping surface wherein all the adjustments are made external to the mold.
2b. Patents of Interest
U.S. Pat. Nos. 3,682,613 to Johnson et al, 4,052,185 to Kolakowski, 4,210,435 to Claassen, 4,274,858 to Claassen et al. and 4,319,907 to Pike disclose press bending mold arrangements. The press faces are metal plates covered with a flexible, heat insulating material that will not harm the glass sheets at elevated temperatures. Adjusting bolts are interposed between the shaping surface and a rigid metal back plate used to reinforce the mold face. A pair of adjusting nuts are positioned along the adjusting bolt on opposite sides of the rigid metal back plate.
U.S. Pat. No. 4,579,577 to Claassen teaches a vacuum mold for shaping hot glass sheets. The mold includes a rigid back plate, a flexible, perforated lower shaping wall and adjustable spacers positioned between the back plate and the shaping wall. Removable side walls are positioned about the perimeter of the mold to seal the mold and form a vacuum chamber.